Human rights campaigners in Russia said yesterday that they were prepared to defend themselves in court after Chechnya's president, Ramzan Kadyrov, announced he was suing over claims that he is a murderer.

Oleg Orlov, head of the Memorial human rights organisation, said he stood by remarks he made last week after the killing of the human rights activist Natalia Estemirova.

Estemirova, 50, was abducted last Wednesday from her home in Chechnya's capital, Grozny. Her body was discovered in the neighbouring republic of Ingushetia. She had been shot in the head and chest.

Estemirova worked for Memorial in Grozny for nearly a decade and documented extrajudicial killings, disappearances and numerous other human rights abuses in the Muslim republic under Kadyrov's rule. She was a close friend of Anna Politkovskaya, the journalist who was shot dead in Moscow in October 2006.

Speaking after Estemirova's killing, Orlov took the rare step of alleging that Kadyrov was her murderer. "We know who is responsible. We know what position he occupies. His job is Chechen president," Orlov told a press conference in Moscow. He said Kadyrov had threatened Estemirova last year and aides had warned her to stop her human rights work or face the consequences.

Kadyrov denies involvement. He claims Estemirova's killing was an attempt to "discredit" Chechnya and Ingushetia. The Russian president, Dmitry Medvedev, has rejected the allegations against Kadyrov, branding them "primitive and unacceptable".

A Russian radio station reported yesterday that Memorial was suspending its work in Chechnya.

Estemirova's murder has provoked international outrage. The German chancellor, Angela Merkel, urged the Kremlin to clarify the circumstances. During a visit to Germany, Medvedev promised the killers would be caught and held to account - a claim most observers treat with scepticism.

Yesterday Orlov said he would not be intimidated by Kadyrov's legal action. He admitted he had no direct proof of Kadyrov's guilt, but said that as a Kremlin-appointed president he bore overall responsibility for events in Chechnya. "I am ready to appear before the court, if there is a trial and to answer for the words I spoke," he told Interfax, the Russian news agency.

There is little prospect that Kadyrov would lose a legal battle, since Russia's courts invariably do what they are told. But the case threatens to heap further damage on the reputation of the Kremlin, for which Kadyrov - a former rebel turned pro-Moscow loyalist - is now a spectacular embarrassment.

Moscow, however, regards him as an indispensable partner and the one leader capable of keeping the lid on a spiralling Islamist insurgency across the North Caucasus.

Activists point out that it is no longer sustainable for Kadyrov to claim that his enemies are responsible for killing his enemies - a strategy used every time a journalist, liberal activist or lawyer opposed to Kadyrov is gunned down in Russia.

"You can't keep on making this claim. It's no longer believable," said one source close to Novaya Gazeta, the paper for which Estemirova also wrote.

On Friday Novaya Gazeta pointed the finger of blame at Kadyrov. In a long article, it recounted the grim circumstances surrounding Estemirova's execution, noting that the white car used to abduct her had been waved through several police checkpoints - only possible if her kidnappers had official ID.

Chechen exiles have alleged that Kadyrov has drawn up a top-secret death list of his enemies, 300 of whom, they say, have been pencilled in for assassination. There is no proof the list exists. In March, however, Umar Israilov, who had complained to the European court of human rights that Kadyrov had personally tortured him, was shot dead in the streets of Vienna.

Another Kadyrov opponent, Sulim Yamadayev, was gunned down in the same month in Dubai.